No evidence for HPAI H5N1 2.3.4.4b incursion into Australia in 2022

There is an ongoing and profound burden of lineage 2.3.4.4b high pathogenicity avian influenza (HPAI) H5 on wild birds and poultry, globally. Herein we report the continued absence of HPAI in Australia from September – December 2022, in inbound migratory birds. Given the ever changing phenotype of this virus, worldwide studies on the occurence, or here absence of the virus, are of critical importance to understand the virus’ dispersal and incursion risk and development of response strategies.

The current high pathogenicity avian influenza (HPAI) H5 panzootic is having a profound impact on the poultry industry and wildlife. 1 While lineage 2.3.4.4b is of current concern, HPAI H5 emerged in poultry in 1996 and has caused outbreaks in wild bird populations episodically since 2005. 2 The epidemiology of this virus has changed substantially with the emergence of new lineages, as exampled by Clade 2 viruses that caused the first wild bird mass mortality event at Qinghai Lake, China in 2005. 3  Understanding viral incursion risk following the emergence of novel lineages of HPAI with their own specific phenotype is of crucial importance in preventing incursion events, improving biosecurity to protect poultry and responding to wild bird outbreaks. The viral incursion into North America in December 2021 was not detected until outbreaks occurred in poultry. 4 The recent incursion into South America, in November 2022, was only detected following mass mortality events. 5 Wild migratory waterfowl have been predominantly implicated in the re-occuring incursions into Europe and Africa. 6 However, there are few migratory waterfowl linking the Nearctic and Palearctic, as well as North and South America, suggesting that the long-distance dispersal of lineage 2.3.4.4b HPAI may rely on additional bird groups other than waterfowl (e.g., Günther et al. 7 ). Lineage 2.3.4.4b has now been detected on all continents except Australia and Antarctica. 8 HPAI incursion risk to Australia has previously been considered low due to the absence of waterfowl species that migrate beyond Australia 9 (Figure 1), as also exemplified from influenza genomic surveillance. 10 Still, annually, millions of migratory seabirds and shorebirds migrate from Asia and North America to Australia ( Figure 1). Some of these species have been shown to be part of the avian influenza reservoir community 11 and potentially survive and move HPAI viruses. 12 To reveal whether a viral incursion may have occurred in As the spatial distribution and intensity of HPAI H5 outbreaks in birds has increased, we have seen a corresponding increase in the number of mammalian cases, including human cases. 1 There has also been indication of mammal-to-mammal transmission for the first time since the emergence of this lineage, 15 such that this avian panzootic has important implications for humans. Australia will again enter a high-risk period when the major bird migrations into the country take place between August and November 2023. Continued surveillance is critical for early detection and rapid response, and as such, we call for enhanced surveillance of Australian wild birds to match heightened incursion risk in the second half of 2023.

CONFLICT OF INTEREST
The authors declare no conflict of interest.

PEER REVIEW
The peer review history for this article is available at https://publons. com/publon/10.1111/irv.13118.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.
F I G U R E 1 HPAI outbreaks along the East Asian Australasian flyway and distributions of key avian influenza reservoir species in Australia. (A) Outbreaks of HPAI in wild birds (red symbols where intensity reflects number of outbreaks at that location) and poultry (blue symbols) since 1 January 2020. Data mined from the World Animal Health Information System of the World Organisation for Animal Health at https://wahis. woah.org/. (B) The East Asian Australasian Flyway utilised by migratory shorebirds. Migratory propensity is exemplified for two populations that we sampled most intensively: Red-necked Stints originally colour-marked in Broome, Western Australia (purple symbols), and Ruddy Turnstones originally marked on King Island, Tasmania (blue symbols). Data extracted from https://www.birdmark.net/. (C) Distribution of Short-tailed Shearwater. Arrow demonstrates southbound migration to Australia occurs from Beringia. (D) Map illustrating the contrasting and limited, Australo-papuan distribution of Australian waterfowl using the distribution of Pacific Black Duck (Anas superciliosa) and Grey Teal (Anas gracilis) as an example. All duck species found in Australia are endemic to Australio-Papuan region and do not migrate to Asia; hence, they are likely to play a nominal role in viral incursions from Asia and were therefore not prioritised in this study.